1. Field of the Invention
This invention relates to a fuel control system for an internal combustion engine, which compensates the amount of fuel supplied during re-starting the engine under high temperatures.
2. Related Art
An internal combustion engine fuel control system is disclosed in Japanese Patent Laid-Open No. 56-81230.
This fuel control system adds and compensates fuel depending on the fuel temperature, engine cooling water temperature and other factors during re-starting of the engine in order to compensate for an insufficient fuel supply. The presence of an insufficient fuel supply is caused by fuel vapor generation during re-starting of the engine, after the engine had been stopped for a lengthy time (e.g., tens of minutes) following being driven under a high load state and under high temperatures.
However, the amount of vapor generated in the fuel supply cannot completely eradicate an excessive or insufficient fuel supply by compensating the fuel supplied to the engine based upon the temperature only. Driving problems such as a rough idle, in which the idling fails to stabilize, cause the engine to stall or malfunction in other ways.
Another example of a known system that includes certain deficiencies is Japanese Patent Laid-Open No. 5-125984.
This fuel control unit proposes compensation by a reduced amount, wherein the path of the negative pressure of the pressure regulator is switched from a suction pipe pressure (internal suction pipe pressure) to a pipe that discharges into the atmosphere so as to raise the fuel pressure. This also restricts the amount of fuel injected and the fuel pressure can drop below the amount which is demanded by the operating condition.
Since compensation control is limited to cases where the negative pressure path of the pressure regulator can be switched from the suction pipe pressure to the discharge pipe to be discharged into the atmosphere, such a device cannot be used on a fuel control unit having no switching mechanism on the negative pressure path. Usually, such devices are designed to maintain a constant fuel pressure against the suction pipe pressure.
The inventors of the present invention have discovered that in the fuel control unit with no switching mechanism on the negative pressure path of the pressure regulator which is designed to maintain a constant fuel pressure against the suction pipe pressure, the amount of generated vapor is influenced by the changes in the fuel temperature as well as the changes in the fuel pressure (an absolute pressure of fuel) relative to the atmospheric pressure. Thus, the present inventors have developed the present invention in order to overcome the disadvantages with the prior art.
Furthermore, although the amount of fuel supplied to an internal combustion engine can be compensated by detecting the fuel pressure relative to the atmospheric pressure by means of a fuel pressure sensor, such a system raises the cost of manufacturing, which is not desirable.